From engine-rear drive power trains with automatic shifting transmissions typically have a park mechanism wherein a "bullet-nose" cam is urged between a reaction wall and a pivotable pawl when the park maneuver is undertaken by the operator. The cam is controlled in axial movement by a linkage connected with the manual selector lever of the transmission.
One such system is shown in Mrlik et al. U.S. Pat. No. 2,875,856 issued Mar. 3, 1959. While systems such as these are very effective, the forces to disengage the cam from between the wall and the pawl can be high when the vehicle is parked on a grade. If systems such as these are used in trucks having a high gross vehicle weight (GVW), the pull-out force can become extremely high, such that considerable effort would be required by the operator when shifting from "Park" to "Drive".